Theofilos A. Papadopoulos

Application of Narrowband Power-Line Communication in Medium-Voltage Smart Distribution Grids

Narrowband power-line communication (PLC) over distribution networks is gaining the attention of researchers, as a communication medium in future power grids. This paper investigates the application of narrowband PLC in smart distribution grids, starting from a historical overview on the accomplished technological progress and continuing with a comparison of the advantages and drawbacks of PLC technology to other smart-grid communication solutions. The analysis shows that narrowband PLC applications are best suitable for medium-voltage (MV) networks, due to the vast and complex geographical extent. The channel and topological characteristics of MV distribution networks are examined for different operational states and configurations, since they are important for the optimal design and implementation of the PLC infrastructure. The analysis is also extended to an existing overhead MV distribution network with distributed-generation units. The obtained results and the proposed methodology are useful and comprehensive tools for the efficient implementation of PLC technology in future smart grids.

Impedances and Admittances of Underground Cables for the Homogeneous Earth Case

A general formulation for the calculation of the influence of the earth return path on the impedances and the admittances of underground multiconductor power cable arrangements is presented in this paper. The expressions for the self and mutual earth correction terms are derived by a rigorous solution of the electromagnetic-field equations. The involved semiinfinite integrals are calculated by using a suitable numerical integration technique. The propagation characteristics of a single insulated conductor and of a typical three-phase single-core cable arrangement are investigated and are compared to the corresponding ones obtained by other approaches. Finally, the cable parameters calculated by the proposed method are used in a simulation of a fast transient in a three-phase single-core cable.

Low-Voltage Distribution Line Performance Evaluation for PLC Signal Transmission

Power-line communications over the low-voltage networks is gaining the attention of researchers in both broadband and narrowband application areas. The transmission characteristics of the power-line carrier are very significant in signal propagation. This paper presents field test and simulation results concerning signal transmission on power lines in underground and aerial installations within the CENELEC EN 50065-1 B band. Field test results show the consistency to the transmission line theory and modal wave propagation. The well-known alternate transients program-electromagnetic transients program (ATP-EMTP) is used for the simulation of the transmission path. Simulation results, obtained for different operational cases and configurations, are compared to the actual measurements from field tests, showing satisfactory agreement. Finally, the proposed models are used in further investigations concerning the signal transmission.

Medium Voltage Network PLC Modeling and Signal Propagation Analysis

PLC technology applications in medium voltage (MV) distribution networks are mainly related to the monitoring, control and metering applications. The CENELEC A band provides adequate transfer rate for such narrow band PLC applications. Scope of this paper is to present simulation results concerning NPL signalling on MV distribution networks. Cases of underground cables, overhead lines and distribution transformers are examined. All simulations have been done using the Electromagnetic Transients Program (ATP-EMTP). Results seem to be consistent with transmission line theory and modal wave propagation, showing standing wave signal voltage profiles along the lines. The case of an aerial MV distribution network is also examined for different frequencies and loading conditions, including open-ended lines, transformers, compensation capacitors and combinations of them.

A Multipath Channel Model for PLC Systems based on Nodal Method and Modal Analysis

One main concern in PLC applications is related to multipath signal transmission and poses certain problems in the prediction of the signal characteristics. In this paper a simple model, suitable for the calculation of the signal voltage and current profiles in cases of multipath PLC channels is proposed. The model is based on the nodal admittance method and can be applied in multiconductor grids, which are decoupled using modal transformations. The model is based on the transverse electromagnetic (TEM) assumption. Several test cases are investigated, including different topologies of a power distribution circuit with the random addition of branches of varying lengths. Phase to phase and phase to ground signal injection cases are examined. The results are checked against the corresponding obtained by the well-known Electromagnetic Transients Program (ATP-EMTP), showing very good agreement.

A PLC based energy consumption management system. Power line performance analysis: Field tests and simulation results

In powerline communications the signal transmission characteristics of the power line carrier are very significant. This paper presents part of the research work done on the development of an integrated Energy Consumption Management System based on powerline communications. Field test results, concerning signal transmission characteristics on power lines in pilot installations are reported. The well known EMTP is used for the simulation of the transmission path. Simulation results, obtained for the no-load and for the full load cases and after the implementation of carrier wave traps, are compared to the actual measurements from field tests, showing satisfactory agreement. The influence of line length and of line terminations is also investigated for both underground cables and overhead distribution lines.

Fair power curtailment of distributed renewable energy sources to mitigate overvoltages in low-voltage networks

Penetration of distributed renewable energy sources in low-voltage (LV) networks is increasing steadily. This trend helps the vision of sustainability, but it is hindered by various economic and technical constraints. Some of the existing solutions put some customers in a disadvantageous position, which is often overlooked while developing technical solutions. In this paper, the most common solutions to cope with overvoltage are analyzed, including inverters with ON/OFF switching and droop-based control features. These two techniques place customers connected to the end of a radial feeder in a disadvantageous position, by curtailing their power generation more than their counterparts who are connected closer to the MV/LV transformer; a situation generally known as unfair power curtailment. In this paper, an efficient solution for voltage rise is proposed, which mitigates voltage rise using conventional droop control techniques, but also provides fair power curtailment among all customers by exploiting the sensitivity matrix of the examined radial feeder. The proposed control strategy is implemented in a flexible simulation platform, based on MATLAB and OpenDSS. Results on different LV networks are compared with the corresponding obtained by conventional droop control methods, highlighting the superior performance of the proposed control strategy.

Sheath voltage calculations in long medium voltage power cables

This paper investigates the operation of single core underground medium voltage cables connected in parallel. The examination is based on an existing power cable arrangement connecting a 38 MW wind farm with the transmission grid. The cable arrangement consists of nine single core cables connected in parallel to form a triple 3-phase system. Several connection scenarios such as the earthing of the cable sheaths at one or both ends and the application of sheath cross-bondings are examined. Various simulation parameters are also investigated such as the grounding resistance of the cable sheaths and the number of the cable sheath transpositions. The respective voltages and currents induced on the cable sheaths are calculated under steady-state and short circuit conditions.

Robust Calculation of Frequency-Dependent Transmission-Line Transformation Matrices Using the Levenberg–Marquardt Method

This paper presents a new method for the calculation of smooth frequency-dependent transmission-line (TL) transformation matrices. The proposed method, based on the Levenberg-Marquardt algorithm, solves an equivalent real-valued approach of the generalized complex eigenproblem. The implemented formulation incorporates a robust convergence criterion and is applicable to all TL configurations, due to the included numerically well-defined computational scheme. Smooth modal transformation matrices are calculated for overhead and underground TL configurations under different representations of the imperfect earth. Results are compared and validated with the corresponding results obtained from the Newton-Raphson and the sequential quadratic programming methods, revealing the accuracy, efficiency, and robustness of the proposed formulation, even in cases where the other methods fail.

Measurement-Based Hybrid Approach for Ringdown Analysis of Power Systems

System identification methods have been widely used for the study of low frequency electromechanical oscillations and the development of low order dynamic models. This paper introduces a hybrid frequency/time-domain approach to estimate the dominant modes contained in ringdown responses of power systems. Practical issues and solutions encountered in the application of the hybrid method are discussed. The performance of the proposed technique is evaluated by applying the Monte Carlo method to synthetic signals and simulated responses from a large-scale power system, as well as to measurements recorded in a microgrid laboratory test facility. Results in all cases proved to be very accurate, verifying the robustness of the proposed method.